The present invention relates to a mass spectrometer and a method of mass spectrometry.
Atmospheric Pressure Photo Ionisation (“APPI”) is a known ionisation technique and is disclosed, for example, in D. B. Robb, T. R. Covey, A. P. Bruins, “Atmospheric Pressure Photoionization: An Ionization Method for Liquid Chromatography-Mass Spectrometry” Anal. Chem. (2000), 72, 3653-3659.
In APPI photons are absorbed by species at atmospheric pressure which have ionization energies or an ionisation potential below the ionisation energy of the photons. For example, a carrier or reagent gas such as nitrogen will strongly absorb vacuum ultra-violet (“VUV”) radiation or UV photons forming an excited metastable species which can then interact with analyte molecules to ionize the analyte molecules:N2+hv→N2*  (1)N2*M→N2+M+·+e−  (2)
Dopant molecules (e.g. toluene and benzene) may also be added in order to increase the ionization efficiency. The dopant molecules readily ionize by photo-ionization and then transfer charge to the analyte molecules. The reagent and dopant ions react with analyte molecules by charge exchange or proton transfer to produce analyte ions.
More recently atmospheric pressure Electron Capture Dissociation (“ECD”) has been demonstrated by creating photoelectrons from excitation of acetone dopant in an APPI source. Reference is made, for example, to D. B. Robb, J. C. Rogalski, J. Kast, M. W. Blades, “A New Ion Source and Procedures for Atmospheric Pressure-Electron Capture Dissociation of Peptides” J. Am. Soc. Mass Spectrom. (2011), 22, 1699-1706.
In a known arrangement ion-ion reactions or ion-radical reactions such as Electron Transfer Dissociation (“ETD”) are performed within an RF ion guide or ion trap and are achieved by producing reagent ions remotely from the ion guide or reaction chamber.
In conventional mass spectrometers reagent ions are generally produced remotely with respect to an RF ion guide and the reagent ions are transferred to the reaction region of the mass spectrometer prior to introduction of analyte ions.
A review of ion-ion reactions was made by S. A. McLuckey and T.-Y. Huang, “Ion/Ion Reactions: New Chemistry for Analytical MS”, Anal. Chem. (2009), 81, 8669-8676.
FIG. 7 of WO 2008/142170 (Scigocki) discloses an arrangement wherein primary ions M+ crossing a central region of a multipolar waveguide are dissociated by Collision Induced Dissociation with background gas so as to form fragment ions m+ and neutral particles m′. The dissociated neutral particles m′ are then directly ionised by laser light from a laser.
U.S. Pat. No. 6,919,562 (Whitehouse) discloses a method of Electron Capture Dissociation (“ECD”) wherein analyte ions are fragmented by interacting analyte ions with low energy electrons.
FIG. 5A of U.S. Pat. No. 6,781,117 (Willoughby) discloses an arrangement wherein a DC collision cell is provided. Reagent gas is ionised by electrons generated from a discharge source. Neutral fragment products are then subsequently ionised by the reagent ions.
It is desired to provide an improved mass spectrometer and method of mass spectrometry.